Vapor separating mechanism



Oct. 11, 1966 R. w. HALBERG ETAL 3,277,632

VAPOR SEPARATING MECHANISM 2 Sheets-Sheet 1 Filed March 19. 1965 Jy DX Oct. 11, 1966 R. w. HALBERG ETAL 3,277,632

VAPOR SEPARATING MECHANISM 2 Sheets-Sheet 2 Filed March 1.9, 1965 United States Patent 3,277,632 VAPOR SEPARATING MECHANISM Robert W. Halherg, Des Plaines, Abraham L. Detwerler,

Barrington, and Renee W. Danforth, Palatine, Ill., as-

signors to Borg-Warner Corporation, Chicago, Ill., a

corporation of Illinois Filed Mar. 19, 1965, Ser. No. 442,853 6 Claims. (Cl. 55-170) This application is a continuation-in-part application of Serial No. 6,946, led February 5, 1960, now abandoned.

This invention relates to a fluid pump adapted to provide a variable volume output at a substantialy constant pressure.

The pump of the present invention is intended to be used particularly as a primary supply pump for a fuel injection system.

This invention constitutes an improvement to an earlier invention disclosed in the application of Abraham L. Detweiler et al., Serial No. 809,807, led April 29, 1959.

The present invention is intended to overcome a major deficiency of earlier pumps of this general type, namely interruption in the fuel liow due to the presence of vapor. The presence of vapor within highly volatile fuels is a problem common to many fuel supply systems and is especially troublesome in fuel injection systems. This is so particularly where optimum performance of the fuel system depends on a minimum fuel supply pressure with a variable demand.

It is desirable to obtain a variable volume output at a substantially constant pressure Without spilling of the pressurized fuel which would lead to further vaporization of the fuel.

The problem of handling vapor present within the fuel pump can be overcome by providing a pump of suicient capacity to pump both fuel and vapor in suicient quantity to meet the demand of the engine. However, in a practical installation, there is a limit to the size, cost, and driving power available for operating the pump.

It is an object of the present invention to provide an improved fluid pump comprising a variable stroke plunger and eccentric driving means for reciprocating the plunger so as to develop a substantially constant pressure, variablevolume output.

It is another object to provide vapor separation means for eliminating vapor from the fuel supplied to the inlet of the pump by the provision of an improved structure which locates the communicating port between the vapor separating cavity and the pump chamber below the vapor separating cavity so that the port will be below the level of the fuel within the vapor separating cavity.

The invention consists of the novel constructions, arrangements, and devices to be hereinafter described and claimed for carrying out the above-stated objects and such other objects as will appear `from the following description of a preferred form of the invention, illustrated with reference to the accompanying drawings wherein:

FIGURE 1 is a longitudinal sectional view of the improved pump of the present invention;

FIGURE 1A is a View taken along the line 1A1A of FIGURE 1;

FIGURE 2 is a View taken along line 2 2 of FIG- URE l;

FIGURE 3 is a view taken along line 3 3 of FIG- URE l;

FIGURE 4 is a view taken on line 4-4 of FIGURE 2; and

FIGURE 5 is a modification of the pump of FIGURE 2 including driving means for a vaccum pump.

Like characters of reference designate like parts in the several views.

Referring to the drawings, the pump of the present invention is designated generally by the numeral 10 and comprises a driving section 11, a pumping section 12, and a vapor separating section 13.

The driving section 11 comprises an electric drive motor 14 having an output shaft 15, and an eccentric driving shaft or crankshaft 16 connected to the output shaft 15 by means of a resilient coupling 17. The eccentric of crankshaft 16 is journaled within a housing 18 by means of a plurality of bearings 19. The housing 18 is attached to a housing 20 for the electric motor 14 by a plurality of machine screws 21. The eccentric shaft 16 extends into a cavity 22 formed within the housing 18 and carries a sleeve 23 journaled on an end of the eccentric shaft 16 by means of a bearing 24.

It is contemplated that the electric motor 14 may be of a compound type that operates at a substantially constant speed under all conditions while still providing a high starting torque.

The pumping section 12 comprises a casing 30 having a stepped longitudinal cylindrical bore 31 and a pumping plunger 32 reciprocably disposed within the bore 31. The pumping plunger 32 carries a spring retainer 33 xedly attached to one end thereof vby means of a screw 34. The screw 34 carries a rubber cap 35 which contacts the driving sleeve 23 on the eccentric drive shaft 16. A spring 36 is disposed under compression within a recess 37 formed in the housing 30 and acts against the spring retaining cap 33. The spring 33 urges the piston 32 to the left as shown during a portion of the pumping stroke. An anti-backlash spring 38 is -also mounted within the cavity 22 and acts against the driving sleeve 23. The spring 38 preferably is formed of a continuous strand of spring material and urges the sleeve 23 and eccentric shaft 16 to the left, as shown, so as to take up any backlash or clearance within the bearings 19 and 24.

The pumping plunger 32 is formed with an enlarged cylindrical head 39 which extends into an enlarged portion of the bore 31. The head 39 separates the enlarged portion of the bore 31 into two pumping chambers designated as 31a and 31b.

The head 39 of the pumping plunger 32 is formed with a stepped cylindrical bore 40 and a longitudinal channel 41 connecting the bore 40 with the chamber 31a. A spring-loaded discharge valve 42 is disposed within the bore 40 and is retained in place by means of an end cap 43 ixedly attached to the head 39. The cap 43 is formed with a central port 44 opening into the chamber 31b. An annular leaf spring inlet valve 45 is disposed adjacent the chamber 31b and admits fuel thereto from a fuel inlet conduit 46. The chamber 31a is connected through an outlet port 47 to a fuel feeding device for an internal combustion engine (not shown).

The vapor separation section 13 comprises a casing portion 50 xedly attached to casing 30 by bolts 50a and formed with an internal cylindrical or tubelike cavity 51. The cylindrical cavity 51 has an axis 51a which is horizontal and parallel to the axis of the movement of the reciprocating plunger 32.

The cylindrical cavity 51 has an angularly offset chamber generally designated 51C having an axis 51bwhich intersects the axis 51a at approximately a 40 angle.

The casing portion has an inlet port 52 for receiving the inlet conduit 46, a vapor barrier portion 53 extending downwardly into the cavity 51, and a vapor release port 55. The fuel inlet conduit 46 is connected to the lowermost portion of a fuel supply tank 56.

The inlet valve 45 comprises a disc 45m disposed within the casing 50 in fluid sealing engagement with the vapor barrier portion 53 as indicated at 45b. Shoulders 45C in the pump casing 30 engage the disc 45a and when bolts 50a are tightened the disc 45a is securely held against vapor barrier 53 to provide a fluid sealing engagement. The disc 45a has ports 54 therein which are disposed on the lower portion of the disc 45a as illustrated in FIG- URE 3. Thus ports 54 are situated in the lower part of the offset chamber 51C of the cylindrical cavity 51 of the vapor separating mechanism. Ports 54 serve a-s the outlet ports from the vapor separating cavity 51 and as the inlet ports to the fluid pumping chamber 31b. As illustrated in FIGURE 3, there are actually three ports 54 formed in the disc 45a to eliminate ilow restriction and insure adequate fluid supply to the pump when required. However, a single large, crescent shaped port or two kidney shaped ports can be used if desired. Also, a complete series of kidney shaped holes extending around the periphery of disc 45a could be used since vapor barrier 53 would close olf those on the top side to provide in effect a disc with openings in the lower half only.

Secured to the disc 45 is an annular leaf spring 45d which functions as a check valve. The spring 45d' allows lluid to ilow from the cavity 51 through ports 54 and into pumping chamber 31b, but when during the pumping cycle the pressure in 31b builds up, the leaf spring 45d will automatically seal off the ports 54 and prevent iluid flow from chamber 31b back into cavity 51 through port 54.

If the disc 45a would be misaligned in assembly so that a section of the ports 54 would be in the upper portion of the disc 45a as disposed in casing portion 50, vapor still could not pass into the pumping chamber 31b since the vapor barrier portion 53 is in iluid sealing engagement with the upper portion of the disc 45a.

By utilization of an offset chamber such as 51C, the outlet port S4 from the cavity 51 is located below the lowest point of the internal surface as indicated at 51d of the cavity 51. Thus assuming the fuel pump and vapor separating mechanism is mounted in an automobile on a 'level road if there is any fuel at all in the cavity 51 the outlet port 54 from the cavity 51 will tend to be below the surface of the fuel and thus help to prevent vapor from being drawn into the pump chamber 31b even though the cavity 51 i-s not completely full of fuel.

The vapor relief port 55 opens into a iluted chamber 57 which is connected through a conduit 58 to an uppermost portion of the fuel supply tank 56. A buoyant valve plug or iloat 59 is disposed within the chamber 57 and is adapted to seal against the port 55. As illustrated in FIG- URES l and 1A the float 59 is centered within the chamber S7 by three flutes 60 formed in the side wall and is prevented from blocking the outlet conduitv 58 by tangs 61 formed on an end of the conduit S8. The tangs are bent in toward the center of chamber 57 to insure engagement with lloat 59.

The iloat 59 is adapted to seal against the port 55 whenever the fuel level in the tank is insulcient to raise the iloat 59 away from the port 55, for instance if the vehicle is on an incline with a small amount of gasoline in the tank. The lloat 59 in a port-blocking position prevents the drawing of air or vapor into chamber 51 from the tank 56 through the conduit 58.

In operation, fuel from the tank 56 is normally supplied by gravity feed through the inlet conduit 46 to the cylindrical cavity 51. The motor 14 is energized so as to set the shaft 15 and eccentric shaft 16 into rotation for reciprocating the pumping plunger 32. During a portion of its stroke, fuel is sucked into the chamber 3111 through the ports 54 in disc 45a. As the eccentric shaft 16 rotates further, the plunger 32 is forced to the right compressing the fuel within the chamber 31h. The annular .leaf spring 45d closes ports 54 and the fuel within the chamber 31h is forced through the discharge valve 42 and channel 41 into the chamber 31a. During the next portion of the pumping stroke, the spring 36 forces the plunger 32 to the left, closing the valve 42 'and forcing the fuel from the chamber 31a through the outlet port 47.

It should be noted that the --pumping section 12 is double-acting inasmuch as fuel is sucked into the cha-rnbcr 31b through the inlet valve 45 at the s-ame time that fuel is being forced out of the cham-ber 31a through the port 47 when the plunger 32 moves to the left. Similarly, during the compression stroke while fuel within the chamber 31h is compressed, half lof the fuel forced from the chamber 31b iills the chamber 31a .and the other half is forced through the outlet port 47, because of the difference in cross sectional area between the head 39 and the body portion of the pumping plunger 32.

The output pressure of the fuel supplied through the port 47 is determined substantially by the strength of the spring 36, and the volume of fuel delivered depends upon the longitudinal displace-ment during each stroke of the pumping plunger 32.

For proper performance of the pumping section 12, it is important that vapor be eliminated from the fuel supplied to the pumping chamber 31b. For this purpose, the barrier portion S3 acts as a baille to separate the bubbles formed by vapor within the fuel from the heavier liquid portion of the fuel. Normally, the pump is operated in the position shown, and the vapor bubbles travel through the port 55, past the float 59, and through the conduit 58 and back to the bank 56. The liquid portion of the fuel passes through ports 54 in disc 45a of inlet valve 45 into the chamber 31h. As previously described, the valve plug 59 acts to seal off the port 55 so as to prevent the entry of air or vapor from the conduit 58 into the inlet valve 45 whenever there is insuilicient fuel in the tank 56 to lloat the plug 59 or when the car happens to be on an incline with -a near empty tank. It is important that the vapor be eliminated at a point immediately adjacent to the uid inlet port to the -pumping chamber so as to prevent the reforming of vapor bubbles in the iluid prior to entering the pump.

The stroke of the pumping plunger is variable, as previously described, in accordance with the fuel demand by the internal fuel combustion engine being supplied.

The spring 36 establishes the noriminal operating pressure of the output fluid, and the force exerted by the spring is balanced by the output pressure acting yagainst the differential area of the head 39 and body portion of the plunger 32. During normal operation, the return stroke of the pumping plunger 32 is, therefore, limited by the output pressure. The limited return stroke of the plunger 32 results in intermittent contact between the drive sleeve 23 and the cap 35 attached to the end of the plunger 32. This intermittent Contact has been found to produce undesirable noise.

The intensity of this noise has been minimized by the following means: (a) the provision of the rubber cap 35 softens the actual contact between the driving sleeve 23 and the plunger 32; (b) the flexible coupling 17 reduces the impact between the sleeve 23 and cap 35 by permitting torsional flexing between the eccentric shaft 16 and output shaft 15 thereby minimizing the effective inertia of the motor armature and extending the time lag in reversing the direction of the pumping plunger 32; and (-c) the spring 38 tends to force the sleeve 23 and eccentric shaft 16 toward the left, as shown, at all times. The action of the spring 3S counteracts the unbalanced forces produced by the eccentric shaft 16 and the eccentrically mounted sleeve 23, thereby substantially preventing radial motion or backlash of the eccentric shaft 16 and sleeve 23 due to clearance within the bearings 19 and 24 at the time of contact.

Referring to FIGURE 5, there is illustrated a modification of the pump of FIGURE 2, incorporating a vacuum pump that is adapted to be driven by the motor 14.

The vacuum pump 70 comprises a casing 71 attached to the casing 18 and formed with a longitudinal cylindrical bore 72 and a piston 73 slidably disposed within the bore 71.2. The bore 72 is adapted to be sealed at one end by a ilapper-type inlet valve 74 which is held in place by an end cap 75. The cap 75 is threaded on the casing 71 and formed with a neck portion 76 .and a longitudinal cylindrical bore 77. The neck portion 76 is adapted to receive a flexible tube or conduit connected to a vacuum reference control for the fuel injection system with which the pump is intended to be used.

The piston 73 is adapted to be reciprocated Within the bore 72 by means of a connecting rod 78 attached to the sleeve 23. The piston 73 is formed with an annular groove 79 which carries a unidirectional sealing ring 80. The casing 71 is formed with an annular groove 81 surrounding the piston 73 and a radial air-discharge port 82.

In operation, the vacuum pump 70 functions as follows: rl`he motor 14 is energized setting the eccentric shaft 16 and sleeve 23 into rotation. The eccentric shaft 16 causes the piston 73 to reciprocate Within the bore 72. During a downstroke, that is when the piston 73 moves to the right, as shown, air is sucked into the bore 72 through the inlet valve 74. During a compression, that is when the piston 73 moves to the left, as shown, the valve 74 closes and air within the bore 72 is compressed. A portion of the air compressed within the bore 72 is forced past the sealing ring 80 and out through the discharge port 82. The sealing ring 80 is in the form of an inverted V in cross section and is unidirectional in operation, that is, it permits the passage of air during the compression stroke but prevents the backward passage of air during the suction stroke.

For the embodiment shown in FIGURE 5, the spring 38 can be eliminated. Once a partial vacuum is established within the bore 77, there will be a net total force acting against the piston 73 tending to move it to the left. The net total force so established acts to eliminate radial motion or backlash due to clearance within the bearings 19 and 24. The vacuum pump 70, therefore, performs the same function as the spring 38 in partially eliminating noise due to backlash within the bearings.

There has been provided by this invention, an improved fuel supply pump adapted to supply a Variable volume output at a substantially constant pressure and that is a practicable size and cost for automotive use.

It will be apparent from the above that applicant has provided an improved vapor separating mechanism for a fuel pump which effectively eliminates vapor from the fuel supplied through use of a vapor barrier which extends downwardly into the cavity of the vapor separating mechanism and guides vapor bubbles into a vapor release port. Further, applicant has provided a new and improved inlet valve to the pump or outlet valve from the vapor separating mechanism which locates the fluid port in communication with the pump and the vapor separating mechanism at the lowest possible point due to the use of an offset construction of the cavity of the separating mechanism so that the uid -communicating port is well below the level of the liquid in the cavity of the vapor separating mechanism.

The novel and improved inlet valve 45 of the subject invention utilizes an effective and economical structure for preventing uid flow from the pumping chamber back into the vapor separating cavity in that an annular leaf spring 45d is secured to the disc 45a of the inlet valve. The spring is effective to seal the communicating port when pressure exists in the pumping chamber and provides a simple solution to the problem of sealing the communicating port at times. Further, the improved structure provided will be effective to serve as a vapor separating mechanism even though the inlet valve may be mislaligned in assembly since the fluid sealing engagement between the vapor barrier portion S3 and the disc 45a of inlet valve 45 will be effective to prevent communication of vapor through any of the ports 54 which mal be disposed in proximity to vapor barrier 53.

Further, applicants have provided an effective oat mechanism which is operative to seal the vapor release port of the vapor separating mechanism whenever there 6 is insufficient fuel in the fuel tank to float the ffoat 59 or when the car happens to be on an incline with a near empty tank.

In summary, the provision of the improved vapor separating mechanism of the present invention in combination with the variable displacement pumping means provides an improved structure which permits .the use of a pump with minimum capacity necessary to supply maximum engine demand and requiring minimum current draw for operating the driving motor.

It is to be understood that the invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claims may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention.

We claim:

1. In a fuel supplying system including a pump having a pumping chamber and a supply tank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in fluid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion and opening into said cavity, an angularly offset chamber extending downwardly with respect to and opening into said cylindrical cavity, means in said offset chamber separa-ting said offset chamber from the pumping chamber, said means having an outlet port through which liquid is supplied to the pumping chamber, conduit means fluidly connecting said vapor release port with said supply tank and through which any vapor bubbles existing in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and said vapor release port comprising means extending downwardly into said offset chamber of said cavity to prevent the passage of vapor bubbles to said outlet port and a buoyant valve responsive to liquid level disposed Within said vapor release port comprising a float blocking said vapor release port when the liquid level in the cavity falls below the level of said vapor release port.

2. In a fuel supplying system including a pump having a pumping chamber and a supply tank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in fluid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion opening into said cavity, an angularly offset chamber extending downwardly with respect to said cavity and opening into said cavity, a valve in said offset chamber having an outlet port through which liquid is supplied to the pumping chamber, a conduit means fiuidly connecting said vapor release port with said supply tank and through which any vapor bubblesexisting in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and said vapor release port comprising means extending downwardly into said offset chamber to prevent the passage of vapor bubbles to said outlet port and a buoyant valve responsive to liquid level disposed within said vapor release port comprising a float blocking said vapor release port when liquid level in the cavity falls below the level of said vapor release port.

3. In a fuel supplying system including a pump having a pumping chamber and a supply tank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in fluid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion opening in to said cavity, an angularly offset chamber extending downwardly with respect to said cavity and opening into said cavity, a valve in said oiset chamber including a disc having an outlet port formed therein through which liquid is supplied to the pumping chamber,

Vconduit means uidly connecting said vapor release port with said supply tank and through which vapor bubbles existing in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and said vapor release port comprising means extending downwardly into said offset chamber of said cavity to prevent the passage of vapor bubbles to said outlet port and a buoyant valve responsive to liquid level disposed within said vapor release port comprising a oat blocking said vapor release port when the liquid level in the cavity falls below the level of said vapor release port.

4. In a system for supplying fuel including a pump having a pumping chamber and a supply Itank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in fluid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion and opening into the upper portion of said cavity, an angularly offset chamber extending downwardly with respect to said cavity and opening into said cavity',

a valve in said offset chamber including a disc having an outlet port through which liquid is supplied to the pumping chamber, spring means on said disc preventing fluid flow from said pumping chamber to said outlet port into said cavity, conduit means fluidly connecting said vapor release port with said supply tank and through which any vapor bubbles existing in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and said vapor release port comprising means extending downwardly into said offset chamber of said cavity to prevent the passage of vapor bubbles to said outlet port and -a buoyant valve responsive to liquid level disposed within said vapor release port comprising a float blocking said vapor release port when the liquid level in the cavity falls below the level of said vapor release port.

5. In a system for supplying fuel including a pump having a pumping chamber and a supply tank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in fluid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion opening into the upper part of said cavity, an angularly olset chamber extending downwardly with respect to said cavity and opening into said cavity, a valve in said offset chamber including a disc having an outlet port through which liquid is supplied to the pumping chamber, an annular leaf spring secured to said disc in operative relation with said outlet port and preventing fluid flow from said pumping chamber into said cavity through said outlet port, conduit means fluidly connecting said vapor release port with said supply tank and through which any vapor bubbles existing in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and vapor release port comprising means extending downwardly into said offset chamber of said cavity to prevent the passage of vapor bubbles to said outlet port and a buoyant valve responsive to liquid level disposed within said vapor release port comprising a float blocking said vapor release port when the liquid level in the cavity falls below the level of said vapor release port.

6. In a system for supplying fuel including a pump having a pumping chamber and a supply tank for supplying fuel to the pump, a vapor separating device operatively associated with said pump comprising a casing portion having a cylindrical cavity therein, said casing portion having an inlet port formed therein in uid communication with said cavity, means connecting said inlet port to said supply tank, a vapor release port formed in said casing portion opening into the upper part of said cavity, an angularly oiset chamber extending downwardly with respect to said cavity and opening into said cavity, a valve in said offset chamber including a disc having an outlet port through which liquid is supplied to the pumping chamber, an annular leaf spring secured to said disc in operative relation with said outlet port whereby said spring will prevent fluid ow from said pumping chamber through said outlet port into said cavity, said outlet port being located in the lower portion of said offset chamber so as to be below the liquid level in said cavity, conduit means uidly connecting said vapor release port with said supply tank and through which any vapor bubbles existing in said cavity will be returned to said supply tank, a vapor barrier disposed between said outlet port and said vapor release port comprising means extending downwardly into said offset chamber of said cavity to prevent the passage of vapor bubbles to said outlet port, said disc being mounted in tluid sealing engagement with said vapor barrier, and a buoyant valve responsive to liquid level disposed within said vapor release port comprising a oat blocking said vapor release port when the liquid level in the cavity falls below the level of said vapor release port.

References Cited by the Examiner UNITED STATES PATENTS 2,213,857 9/1940 Gritiith 55-169 2,217,655 10/1940 Bassett 55-159 2,368,524 1/1945 Dach. 2,582,105 1/1952 Bassett 55-159 2,959,135 11/1960 Dermond 251-75 REUBEN FRIEDMAN, Primary Examiner.

' SAMIH N. ZARHARNA, Examiner.

J. ADEE, Assistant Examiner. 

1. IN A FUEL SUPPLYING SYSTEM INCLUDING A PUMP HAVING A PUMPING CHAMBER AND A SUPPLY TANK FOR SUPPLYING FUEL TO THE PUMP, A VAPOR SEPARATING DEVICE OPERATIVELY ASSOCIATED WAITH SAID PUMP COMPRISING A CASING PORTION HAVING A CYLINDRICAL CAVITY THEREIN, SAID CASING PORTION HAVING AN INLET PORT FORMED THEREIN IN FLUID COMMUNICATION WITH SAID CAVITY, MEANS CONNECTING SAID INLET PORT TO SAID SUPPLY TANK, A VAPOR RELEASE PORT FORMED IN SAID CASING PORTION AND OPENING INTO SAID CAVITY, AN ANGULARLY OFFSET CHAMBER EXTENDING DOWNWARLY WITH RESPECT TO AND OPENING INTO SAID CYLINDRICAL CAVITY, MEANS IN SAID OFFSET CHAMBER SEPARATING SAID OFFSET CHAMBER FROM THE PUMPING, CHAMBER, SAID MEANS HAVING AN OUTLET PORT THROUGH WHICH LIQUID IS SUPPLIED TO THE PUMPING CHAMBER, CONDUIT MEANS FLUIDLY CONNECTING SAID VAPOR RELEASAE PORT WITH SAID SUPPLY TANK AND THROUGH WHICH ANY VAPOR BUBBLES EXISTING IN SAID CAVITY WILL BE RETURNED TO SAID SUPPLY TANK, A VAPOR BARRIER DISPOSED BETWEEN SAID OUTLET PORT AND SAID VAPOR RELEASE PORT COMPRISING MEANS EXTENDING DOWNWARDLY INTO SAID OFFSET CHAMBER OF SAID CAVITY TO PREVENT THE PASSAGE OF VAPOR BUBBLES TO SAID OUTLET PORT AND A BUOYANT VALVE RESPONSIVE TO LIQUID LEVEL DISPOSED WITHIN SAID VAPOR RELEASE PORT COMPRISING A FLOAT BLOCKING SAID VAPOR RELEASE PORT WHEN THE LIQUID LEVEL IN THE CAVITY FALLS BELOW THE LEVEL TO SAID VAPOR RELEASE PORT. 